Problem in inserting a part as the first part of an assembly

I used File->New and chose Assembly. SW asked me to select a component to insert, I chose a .prt file and got "Failed to open file." I went to File->Open to open the same .prt file, I got the Import Diagnostics window, clicked yes and got "No faulty faces or gaps remain in the geometry." Clicked the check mark, nothing showed up on the screen. On the three, there are only: sensors, annotations, material, front plane, top plane, right plane, origin and a DIMMED Imported 1. Know what is going on?

When I opened the step version of the same design, I could open it fine. How could I put it as the first part of my new Assembly? I want the center of this part to be the center of my more complicated assembly. Thanks.

SolidworksGeneral